The present invention relates generally to vehicles, and more particularly to a method for determining axle load of a vehicle.
Conventional methods for determining axle load of a moving vehicle include determining the axle load on a tire through the use of vehicle ride height sensors located at each wheel. The vehicle height sensors are generally a part of a relatively-expensive controlled vehicle suspension system.
What is needed is an improved method for determining axle load of a moving vehicle.
A first method of the invention is for determining the axle load on a rotating tire of a moving vehicle and includes steps a) through e). Step a) includes empirically determining a first relationship between the pressure of a test tire and the rolling radius of the test tire at a constant axle load on the test tire, wherein the pressure is measured by a pressure sensor, and wherein the rolling radius is determined from the measured rotational speed of the test tire. Step b) includes empirically determining a second relationship between the axle load on the test tire and the rolling radius of the test tire at a constant pressure of the test tire, wherein the axle load is a measured axle load, and wherein the rolling radius is determined from the measured rotational speed of the test tire. Step c) includes, after steps a) and b), taking a measurement of the pressure of the rotating tire using a pressure sensor. Step d) includes, after steps a) and b), taking a measurement of the rotational speed of the rotating tire. Step e) includes determining the axle load on the rotating tire from the measurements of steps c) and d) and from the first and second relationships of steps a) and b).
A second method is for determining the percent axle load of a first axle of a moving vehicle having first and second axles and includes steps a) through e). Step a) includes empirically determining a first relationship between the pressure of a test tire and the rolling radius of the test tire at a constant axle load on the test tire, wherein the pressure is measured by a pressure sensor, and wherein the rolling radius is determined from the measured rotational speed of the test tire. Step b) includes empirically determining a second relationship between the axle load on the test tire and the rolling radius of the test tire at a constant pressure of the test tire, wherein the axle load is a measured axle load, and wherein the rolling radius is determined from the measured rotational speed of the test tire. Step c) includes, after steps a) and b), taking a measurement of the pressure of a first tire on the first axle using a pressure sensor and taking a measurement of the pressure of a second tire on the second axle using a pressure sensor. Step d) includes, after steps a) and b), taking a measurement of the rotational speed of the first tire and taking a measurement of the rotational speed of the second tire. Step e) includes determining the percent axle load of the first axle from the measurements of steps c) and d) and from the first and second relationships of steps a) and b).
A third method of the invention is for determining the axle load on a rotating tire of a moving vehicle and includes steps a) through c). Step a) includes empirically determining a relationship between the axle load on a test tire and the rolling radius of the test tire at a constant pressure of the test tire, wherein the axle load is a measured axle load, and wherein the rolling radius is determined from the measured rotational speed of the test tire. Step b) includes, after step a), taking a measurement of the rotational speed of the rotating tire. Step c) includes determining the axle load on the rotating tire from the measurement of step b) and from the relationship of step a).
A fourth method of the invention is for determining the percent axle load of a first axle of a moving vehicle having first and second axles and includes steps a) through c). Step a) includes empirically determining a relationship between the axle load on a test tire and the rolling radius of the test tire at a constant pressure of the test tire, wherein the axle load is a measured axle load, and wherein the rolling radius is determined from the measured rotational speed of the test tire. Step b) includes, after step a), taking a measurement of the rotational speed of a first tire on the first axle and taking a measurement of the rotational speed of a second tire on the second axle. Step c) includes determining the percent axle load on the first axle from the measurements of step b) and from the relationship of step a).
Several benefits and advantages are derived from one or more of the methods of the invention. Determining axle load from tire rotational speed measurements or from tire rotational speed and tire pressure measurements is less expensive than using a conventional and relatively-expensive vehicle ride height sensor located at a wheel. Having axle load information easily available allows such information to be used to control the vehicle as with conventional vehicle control systems employing, or adapted by using a method of the invention to employ, axle load inputs.